At first, Threadbox offered a personal assistant app to help you organize your email. In March, it broke free of email and relaunched as a standalone collaboration tool. And now it’s actually offering to replace your email and instant messenger accounts.

Threadbox (which launched under its old name Cc:Betty at VentureBeat’s DEMO conference in spring 2009) is a site where you can have searchable real-time conversations. When chief executive Michael Cerda gave me a demonstration, I was impressed with how easy it seemed to manage different conversations and drill down on different kinds of content.

The Palo Alto, Calif. company calls its new email replacement feature Threadbox Messenger. You can sign up for @threadbox email accounts, and messages sent to that account are automatically pulled into Threadbox. Other new features include the ability to invite any of your contacts from Gmail, Facebook, Twitter, or LinkedIn to a thread, to hold one-on-one conversations in a private thread, to share links to threads, and to receive notifications on your computer desktop when there’s Threadbox activity.

Threadbox now has 50,000 users spread out among 20,000 businesses, Cerda said. He added that a number of Threadbox users are already seeing the service as an email and IM replacement, so this is a logical next step.

The company has raised $2 million in funding. Threadbox was planning to raise more funding this fall, Cerda said, but it has also been approached by bigger companies as a possible acquisition target. Not surprisingly, Cerda declined to get specific about who’s making those offers.

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